Variable-speed portable electric tools



Am 15, E967 J. P. YELPO ETAL 3,336,490

VARIABLE-SPEED PORTABLE ELECTRIC TOOLS 2 Sheets-Sheet 1 Original Filed April 20, 1964 INVENTORS- JOSEPH P YELPO and DON BWINCHESTER ATTORNEY WITNESS Aug. 15, W7 J. P. YELPO ETAL VARIABLE-SPEED PORTABLE ELECTRIC TOOLS 2 Sheets-Sheer. 2

SUPPLY Original Filed April 20, 1964 m T m 0 E T W Y NP E VEW W WW N A W0 D S O J United States Patent 1 Claim. (Cl. 310-50) This application is a continuation of application Ser. No. 361,169, now abandoned.

This invention relates to variable-speed portable electric tools and more particularly to portable tools driven by built-in electric motors and having all-electric built-in circuitry for providing, by external manual adjustment, a plurality of selective regulated speeds for said motors.

It is a problem with portable tools of this type to provide a sufficiently compact physical arrangement of the required circuitry which is, at the same time, electrically safe and mechanically secure and which may readily be assembled within the small space available and connected to the motor and switch without interference with the other parts of the tool and without appreciably increasing the size and weight of the tool and the difficulty of assembly.

This problem has been solved according to the present invention by providing compact prewired circuit modules electrically interconnected by flexible conducting leads to form a unitary subassembly and a removable cover for the handle end of the tool, which cover, when removed, completely exposes the interior of the tool housing throughout an entire cross section thus giving open access for readily installing each of the prewired circuit modules therein in a position to be subsequently resiliently clamped in place by the cover when it is secured to the motor housing as a final assembly step.

It is therefore a primary object of this invention to provide special structure which results in a low-cost assembly of physical circuit components within the housing of a portable electric tool to adapt said tool for operation at a plurality of selected regulated operating speeds.

It is a further object of this invention to subdivide a physical circuit into separate but flexibly connected circuit modules for optimum positioning said modules in a portable electric tool in accordance with the functions of said modules thus to provide minimum space requirements consistent with adequate insulation safety.

With the above and other objects in view, as will hereinafter appear, the invention comprises the devices, combinations and arrangements of parts hereinafter set forth and illustrated in the accompanying drawings of a preferred embodiment of the invention, from which the several features of the invention and the advantages attained thereby will be readily understood by those skilled in the art.

In the drawings, FIG. 1 is a longitudinal sectional view taken through a portable electric tool showing a preferred embodiment of the invention.

FIG. 2 is a vertical transverse section taken substantially on line 2-2 of FIG. 1.

FIG. 3 is a detailed section taken substantially on line 3-3 of FIG. 2.

FIG. 4 is a schematic diagram showing the circuit configuration corresponding to the physical arrangement shown in FIGS. 1 and 2.

Referring now to FIG. 1, there is shown a portable tool, preferably an electric drill, having a motor housing 10, 8. depending split handle portion 11, and a removable cover portion 12 which when removed exposes the interior of the tool throughout preferably an entire cross section as seen best in FIG. 2. The parting line between the cover and the remainder of the tool is indicated by line 13.

The motor housing 10 is formed with an end bracket portion 14 having a boss 15 in which is received a ball bearing 16 for journaling a shaft 17 of a motor armature 18. Brush boxes 19-19 are also carried by the motor housing 10 and contain brushes 20-20 which bear on a commutator 21. A field core 22 secured in the motor housing 10 surrounds the armature 18 and is provided with field winding 23. Apertures 40 in the housing 10 on either side of the end bracket portion 14 provide access for bringing out conducting leads from the brushes 20 and from the field windings 23 for making electrical connections to the circuit modules to be described subsequently.

Referring now to FIG. 4 the circuit configuration used to illustrate an embodiment of this invention is the fullwave version of the circuit shown and described in the Momberg et al. Reissue Patent No. 25,203 issued July 24, 1962. The circuit is physically divided into two separate circuit modules, viz a power module 24 and a control module 25', as shown by the dot-dash lines. These modules 24, 25 are permanently and electrically interconnected by the fiexible conductors 26 and 27. The power module consists of four silicon rectifiers 28 of the push-in type poled as shown in a conventional full-wave bridge configuration. The rectifiers 28 as seen in FIGS. 1 and 2 are mounted in pairs on two electrically conducting brackets 29-29 secured in spaced relation to an insulation board 30. The brackets are drilled and tapped to accept screws 31 for connecting respectively to conductor 32 which connects to one side of the A.C. supply and to conductor 33 which connects to a switch 34 and thence by a conductor 35 to the other side of the A.C. supply. A third conductor 36 connects to the tool housing at screw 37 for external grounding as shown. All three conductors 32, 35 and 36 are cabled to form a power cord and are contained within a strain-relief bushing 38.

A single screw 39 passes through an aperture in the cover 12 and is threaded into the split handle portion 11 to secure these parts together to form a complete handle. This same screw 39 also secures the power module 24 resiliently in position within the handle by virtue of an insulated spacer bushing 41 seated in a boss 42 and surrounding the screw 39, which bushing receives a resilient insulated plug 43 also surrounding the screw 39 and bearing against one side of the board 30. As screw 39 is taken up to secure parts 11 and 12 together, the board 30 is resiliently clamped between the plug 43 and a boss 44 formed on the interior of cover 12. A piece of stiff insulation 45 placed between the board 30 and the boss 44 covers any metallic elements such as rivets which may be used to secure the brackets 29 to the board 30. The board 30 is further secured against turning by means of cut-away portions 46-46 which closely fit against bosses 47-47 formed on the interior of cover 12 as shown in FIG. 2.

The switch 34 having trigger 48 and lock button 49 is received in suitable bosses 50 in the cover 12 and is held captive by securement of the lock-button bearing element 51 of the switch 34 on the parting line 13 and clamped between the handle portion 11 and the cover 12. The trigger 48 is slidable in a slotted aperture in the handle portion 11.

The control module 25 comprises an insulated circuit board 52 having the general configuration of the cross section of the cavity behind the motor housing 10 and mounts on one side several electrical components which are interconnected on the reverse side preferably by a conventional printed circuit which follows the diagram shown in FIG. 4.

A voltage divider is formed by the series connection of a fixed resistor 53, a speed setting potentiometer 54, and a trimmer potentiometer 55. A silicon controlled rectifier 56 is mounted on a bracket 57 which is secured to and is electrically connected to anode stud 58. The bracket 57 is clamped between the stud flange 59 and a finned heat sink 60 surmounting the stud 58 by means of a screw 61 threaded onto the stud 58. The bracket 57 is secured to the board 52, makes contact with the printed circuit on the reverse side and is formed with a tab portion 62 which receives a push-on terminal 63 connected to a conducting lead 64 from the field winding 23. The other end of the field winding 23 is connected by conducting lead 65 terminating in push-on terminal 66 which engages a tab 67 secured to the board 52. A back rectifier diode 68 is connected across the field winding 23 and is poled as shown.

Leads 69 and 70 permanently secured to the board 52 pass through apertures 40 to connect with brushes 2020. A connection is made by way of the printed circuit from the slider of the speed setting potentiometer 54 through a diode 71 to the gate 72 of the controlled rectifier 56. An electrolytic capacitor 73 is connected across the gate 72 and cathode 74 of the controlled rectifier as shown.

The end bracket portion 14 is formed with bosses 75-75 as seen best in FIG. 3. These bosses 7575 are formed with shouldered locating pins 76-76 which receive mating cut-out portions 7777 in the board 52 for locating said board in proper position to receive screws 7878 which extend through the cover 12 and are threaded into bosses 7979 formed on the bracket portion 14. Rubber grommets 8080 received in cut-out portions 8989 of the board 52 are clamped between the cover 12 and the bosses 79 when the screws 78 are taken up to secure the cover 12. A resilient bumper plug 81 may be inserted in an apertured boss 82 to provide, together with the grommets 80, a three-point resilient suspension for the board 52.

An insulation piece 91 is placed between the board 52 and the bearing boss 15 to protect the printed circuit against contact with tool ground.

The speed setting potentiometer 54 is secured to the board 52 and has a shaft 83 secured to which is a knob 84 which extends through an aperture 85 in the cover 12 for manipulation externally of the tool as shown best in FIG. 1.

The trimmer potentiometer 55 has a stub shaft 86 formed with a screw-driver slot 87 which shaft may be adjusted as a final factory circuit setting by a special trimming tool inserted through a ventilating slot 88 in the cover 12. This adjustment sets the minimum motor speed.

From the above it will be perceived that there has been provided according to this invention a compact arrange- 4 ment of prewired and preconnected circuit modules for simple assembly in and connection to the motor of a portable electric tool and with resilient securement of the modules being effected by the same means as used to secure the cover in the final assembly step.

It will also be perceived that, by subdividing the circuit into two separate circuit modules in accordance with the module function and by shaping each module to conform to the desired space location within the tool, the modules may then be placed in spaced positions within the tool so that the conducting leads from the power cord, the switch and the motor windings may be made short and direct so as to make optimum use of the available space and to simplify the assembly.

Having thus described the nature of the invention, what we claim herein is:

A multi-spee-d portable electric tool having a motor housing and a depending split handle portion comprising:

(a) a hollow cover removably secured to said motor housing and to said handle portion and providing;

(b) a first cavity located adjacent said motor housing and (c) a second cavity interconnected with said first cavity and forming with said handle portion a hollow handle,

(d) an electric motor secured in said housing and having an armature winding and a field winding,

(e) a first circuit module including semiconductor rectifiers connected in a full-wave bridge circuit and mounted on a single insulated support clamped between the cover and the handle portion in the second cavity,

(f) a second circuit module including a semiconductor controlled rectifier connected in a speed control circuit and mounted on a single insulated support clamped between the cover and the motor housing in the first cavity,

(g) said circuit modules being electrically interconnected by flexible conductors to form a unitary subassembly,

(h) electrical conducting means for connecting said second circuit module with said armature and field windings,

(i) a switch, and

(j) a power cord secured in said hollow handle, and

(k) means for electrically connecting said first circuit module with the switch and with the power cord.

No referencescited.

,MILTON O. HIRSHFIELD, Primary Examiner.

J. D. MILLER, Assistant Examiner. 

